Structure ()f Recent and Fossil Conifer a. Sll 



Jar form, for, as in the Moreton Bay species, the meshes assume 

 very different forms in different parts. 



In the longitudinal section parallel to a radius, the discs op 

 areolae of the Araucaria excelsa are similar in every respect to 

 those of the Moreton Bay species ; but whilst in the latter, as fur 

 as my observations have extended, they most frequently occur 

 in single rows, in the former they most frequently occur in 

 double rows. In the excelsa, triple rows are often to be seen ; 

 and in these as well as in the double rows, the polygonal por- 

 tions of the discs are well defined. In many of the triple rows, the 

 discs of the middle row have the most perfectly regular hexago- 

 nal form. The side-rows have their polygonal parts equally well 

 defined and rectilinear; and in both the triple and double rows, the 

 contiguous sides of the discs are connected with each other, 

 by two fine lines or fibres,. at or near each of the angles. To see 

 these connecting lines distinctly, a very strong light is required. 

 The form of the discs, both in the double and triple rows, in- 

 tirely depends on the distance of the discs from each other. 

 When the discs are at a certain distance, the form is polygonal ; 

 but when the distance is a little greater, the form is circular. 



When a section has been cut of the proper thickness, the 

 discs display at the circumference two very distinct concentric 

 curves when the form is circular, and two distinct lines on each 

 of the straight sides when the form is polygonal. At the cen- 

 tre there is always a circular opening, and surrounding this 

 several concentric curves may often be seen, whether the form 

 be circular or polygonal. The discs often appear of a pretty 

 uniform brownish-red colour, without shewing any concentric 

 curves near the centre, or double lines at the circumference, dei. 

 pending apparently on the thickness of the slice. When the 

 slice is very thin, many of the discs display no colour at all, 

 and merely present two curves, one at the centre and another at 

 the circumference. A whole row of discs, too, is sometimes to 

 be seen lying in a plane very much inclined to that of the sec- 

 tion containing it. In such cases the discs present their edges 

 to the eye with a slight degree of obliquity, and shew that their 

 thickness bears a very small proportion to their diameters. 



The discs, whether in single, double, or triple rows, are al- 

 ways placed near one another, and never occur dispersed at 



